Kim Nguyen, a 62-year-old seamstress from Vietnam who has lived in Tennessee since 1975, had a persistent fever and infections throughout her bones.

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The patients' immune systems become damaged, leaving them unable to fend off germs as healthy people do. What triggers this isn't known, but the disease does not seem to be contagious.

This is another kind of acquired immune deficiency that is not inherited and occurs in adults, but doesn't spread the way AIDS does through a virus, said Dr. Sarah Browne, a scientist at the National Institute of Allergy and Infectious Diseases.

She helped lead the study with researchers in Thailand and Taiwan where most of the cases have been found since 2004. Their report is in Thursday's New England Journal of Medicine.

"This is absolutely fascinating. I've seen probably at least three patients in the last 10 years or so" who might have had this, said Dr. Dennis Maki, an infectious disease specialist at the University of Wisconsin in Madison.

It's still possible that an infection of some sort could trigger the disease, even though the disease itself doesn't seem to spread person-to-person, he said.

The disease develops around age 50 on average but does not run in families, which makes it unlikely that a single gene is responsible, Browne said. Some patients have died of overwhelming infections, including some Asians now living in the U.S., although Browne could not estimate how many.

Kim Nguyen, 62, a seamstress from Vietnam who has lived in Tennessee since 1975, was gravely ill when she sought help for a persistent fever, infections throughout her bones and other bizarre symptoms in 2009. She had been sick off and on for several years and had visited Vietnam in 1995 and again in early 2009.

"She was wasting away from this systemic infection" that at first seemed like tuberculosis but wasn't, said Dr. Carlton Hays Jr., a family physician at the Jackson Clinic in Jackson, Tenn. "She's a small woman to begin with, but when I first saw her, her weight was 91 pounds, and she lost down to 69 pounds."

Nguyen (pronounced "when") was referred to specialists at the National Institutes of Health who had been tracking similar cases. She spent nearly a year at an NIH hospital in Bethesda, Md., and is there now for monitoring and further treatment.

"I feel great now," she said Wednesday. But when she was sick, "I felt dizzy, headaches, almost fell down," she said. "I could not eat anything."

AIDS is a specific disease, and it stands for acquired immune deficiency syndrome. That means the immune system becomes impaired during someone's lifetime, rather than from inherited gene defects like the "bubble babies" who are born unable to fight off germs.

The virus that causes AIDS — HIV — destroys T-cells, key soldiers of the immune system that fight germs. The new disease doesn't affect those cells, but causes a different kind of damage. Browne's study of more than 200 people in Taiwan and Thailand found that most of those with the disease make substances called autoantibodies that block interferon-gamma, a chemical signal that helps the body clear infections.

Blocking that signal leaves people like those with AIDS — vulnerable to viruses, fungal infections and parasites, but especially micobacteria, a group of germs similar to tuberculosis that can cause severe lung damage. Researchers are calling this new disease an "adult-onset" immunodeficiency syndrome because it develops later in life and they don't know why or how.

"Fundamentally, we do not know what's causing them to make these antibodies," Browne said.

Antibiotics aren't always effective, so doctors have tried a variety of other approaches, including a cancer drug that helps suppress production of antibodies. The disease quiets in some patients once the infections are tamed, but the faulty immune system is likely a chronic condition, researchers believe.

The fact that nearly all the patients so far have been Asian or Asian-born people living elsewhere suggests that genetic factors and something in the environment such as an infection may trigger the disease, researchers conclude.

The first cases turned up in 2004 and Browne's study enrolled about 100 people in six months.

"We know there are many others out there," including many cases mistaken as tuberculosis in some countries, she said.

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